Hello, My name is John
If you only have 1 key you can't program any other keys or re-program the one you have.
So I assume you can't start the car?
Does the theft light flash fast when you try to start the engine?
OK, so with only one key you would need to use a scan tool with "PATS" functionality to try to reprogram the key. It is not likely the key has lost its programing. You could have a bad key, or a concern with the PATS system.
I would recommend getting 2 news keys and attempt to program them.
If I can provide you with any other information please fell free to ask.